title: Irradiation with ultraviolet light and gamma-rays increases the level of DNA topoisomerase II in nuclei of normal and xeroderma pigmentosum fibroblasts.
abstract: DNA topoisomerase II was monitored with the monoclonal antibody Ki-S1 in human fibroblasts after irradiation of cells with 254-nm UV light and -rays from a 137Cs source. DNA topoisomerase II was localized immunohistochemically as bright fluorescent dots in the karyoplasm. Investigated fibroblasts originated from normal human donors and a xeroderma pigmentosum patient (XP12BE). All cell lines showed a time and dose-dependent increase in DNA topoisomerase II abundance after irradiation. The increase may reflect enhanced accessibility of the enzyme, enhanced gene expression or enhanced stabilization of mRNA or protein molecules. The effect was detectable as early as 1 h after irradiation at doses 3 J/m2 or 3 Gy. It passed through a maximum and decreased within 18 h (UV light) or 6 h ( -rays). Except for the duration of the response, no principal differences were seen between the effects caused by UV light and those elicited by -rays. The increase in enzyme levels might be part of the well-known DNA damage responses which operate in cell-protective or DNA-reparative pathways or may reflect initiation of apoptosis. DNA topoisomerase I was detected with a commercially available polyclonal antibody raised against human DNA topoisomerase I. In unirradiated cells, DNA topoisomerase I was found to be mainly concentrated in nucleoli. Irradiation with -rays changed the staining pattern in that it caused a multitude of DNA topoisomerase I-rich centers to occur which may reflect sites of transcription of radiation-inducible genes.
authors.affiliation: German Cancer Research Center, Division of Interaction of Carcinogens with Biological Macromolecules, Im Neuenheimer Feld 280, Heidelberg, D-69120, Germany.
authors.forename: H W
authors.initials: HW
authors.lastname: Thielmann
authors.forename: O
authors.initials: O
authors.lastname: Popanda
mesh_terms: D017209:Apoptosis / Q000502:physiology; D002588:Cesium Radioisotopes; D004249:DNA Damage / Q000502:physiology; D004260:DNA Repair; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000201:enzymology / Q000528:radiation effects*; D005720:Gamma Rays; D006801:Humans; D007150:Immunohistochemistry; D014158:Transcription, Genetic; D014466:Ultraviolet Rays; D014983:Xeroderma Pigmentosum / Q000201:enzymology* / Q000473:pathology
chemical_list: D002588:Cesium Radioisotopes; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II